Adaptation to lower latitudes and lower elevations precedes the evolution of hummingbird pollination in western North American Penstemon

Premise: A switch in pollinator can occur when a plant lineage enters a
new habitat where the ancestral pollinator is less common and a novel
pollinator is more common. Since pollinator communities vary according to
environmental tolerances and availability of resources, there may be
consistent associations between pollination mode and specific regions and
habitats. Such associations can be studied in lineages that have
experienced multiple pollinator transitions, representing evolutionary
replicates. Methods: Our study focused on a large clade of Penstemon
wildflower species in western North America that has repeatedly evolved
hummingbird-adapted flowers from ancestral bee-adapted flowers. For each
species, we estimated geographic ranges from occurrence data and inferred
environmental niches from climate, topographical, and soil data. Using a
phylogenetic comparative approach, we investigated whether
hummingbird-adapted species occupy distinct geographic regions or habitats
relative to beeadapted species. Results: Hummingbird-adapted species occur
at lower latitudes and lower elevations than bee-adapted species,
resulting in a difference in their environmental niche.
Hummingbird-adapted species seem to evolve in lineages that previously
adapted to lower latitudes and elevations, since bee-adapted species
sister to hummingbird-adapted species also occur in these regions and
habitats. Sister species pairs – regardless of whether they differ in
pollinator – show relatively little geographic range overlap. Conclusions:
Adaptation to a novel pollinator may often occur in geographic and
ecological isolation from ancestral populations. The ability of a given
lineage to adapt to novel pollinators may critically depend on its ability
to colonize regions and habitats associated with novel pollinator
communities.